1. Field of the Invention
This disclosure relates to the field of residue detection. In particular, to the automatic detecting of residues of substances present in letter mail while the mail is in a postal facility.
2. Description of the Related Art
Since the use of Anthrax in the United States Mail in October 2001, government organizations have becoming increasingly interested in detecting dangerous substances such as microorganisms, chemicals, or biological warfare agents which could be distributed through the mail system to promote the agenda of a terrorist organization. As the postal service and mail delivery is a virtually universal service touching the lives of almost all people throughout the United States and many more throughout the world, the postal service presents a potentially limitless distribution network for a terrorist group to utilize. Further, by the time a letter or package has reached the final destination, it has often been handled by many individuals, some of whom may not be known without a lengthy investigation. Any or all of these individuals may have been exposed to the substance and could be affected without rapid medical response. Further, in the case of a contagious substance, trying to quarantine those exposed prior to the contagion becoming epidemic may be virtually impossible.
October 2001 was not the first use of the mail for terrorist acts. Mail bombs and even dangerous pranks were common long before the mail was used as a method for distributing a biological warfare agent. In addition to purposeful terrorist acts, sometimes dangerous substances are shipped in the mails innocently or for other purposes. Dangerous substances may be shipped by a person who simply does not think of the consequences or the mail may be utilized for other illicit acts such as drug trafficking.
In order to allow the mail to be secure to parties using the mail system for legitimate purposes, mail is sealed and the contents are generally inaccessible to postal workers. This confidentiality is necessary as much of the mail includes confidential information such as financial information and the like and mail which was open could lead to theft of financial information and other important information. At the same time, the sealing of mail can make it difficult for a contaminant to be detected until the mail has reached its prescribed destination.
For the most part, there are no systems designed to screen mail, particularly letters and flats, for contaminants. Existing systems are often limited to large boxes and packages and can only screen for items which can show up on x-ray or similar scanners. These systems, while often effective for detecting bombs, are generally unable to detect powders, liquids, or similar substances which are unlikely to show up on the scans. Oftentimes, the defense to using the mails for terrorist acts is simply to expose the mail to powerful radiation or other decontaminants in the hopes of neutralizing any biologicals present, but this cannot protect against chemical agents and can also damage mail documents. Further, such irradiation is often performed after mail is sorted to protect the recipient, but there may have been many exposed prior to this step.